Chemical based paint removers (also referred to as “paint strippers”) have enjoyed widespread commercial application due to their relative ease of use when compared to various physical methods of paint removal, such as scraping and sanding. Many of these paint removers are solvent based, utilizing methylene chloride, methanol, acetone, toluene, xylene or other solvent components. While these solvents yield significant paint removal, they may also present potential health, safety and environmental concerns to both the user and the surrounding environment.
U.S. Pat. No. 2,507,983 discloses a paint stripper which contains methylene chloride and methyl cellulose, which is a thickening agent used to increase the viscosity of the formulation. Methylene chloride is an effective low cost paint stripper characterized by high vapor pressure (400 mm Hg at 75° F.) which causes the methylene chloride to evaporate very rapidly. This high vapor pressure may lead to a vapor inhalation hazard. In addition, methylene chloride is a suspected carcinogen as well as a dermal irritant. A further concern of methylene chloride is possible ground water contamination when the residual stripper is removed from the substrate.
In an effort to reduce the health, safety and toxicity concerns related to methylene chloride based paint strippers, several formulations utilizing N-methyl-2-pyrrolidone (NMP) have been developed. Because of its effectiveness, low toxicity, biodegradability and high flash point, NMP has been proposed as a substitute for chlorinated solvents. For example, U.S. Pat. Nos. 4,120,810; 4,666,626; 4,749,510; 4,812,255; 5,006,279; and 5,049,300 disclose paint stripping compositions which include NMP and other components, such as aromatic hydrocarbons or aromatic solvents.
These and other formulations, however, may still present potential health, safety and dermal hazards based on the absorption rate of the particular aromatic hydrocarbon or aromatic solvent used. In addition, many aromatic hydrocarbons are believed to be carcinogenic, pose environmental concerns and are troublesome regarding disposal of spent chemical.
U.S. Pat. No. 5,011,621 relates to mixtures of NMP, selected co-solvents (which may include aromatic hydrocarbons and terpenes such as d-limonene), as well as animal and/or vegetable oil, as a means to effectively remove paint from substrates. However, the presence of one or more of these natural components, such as tallows and fatty acids, may lead to the growth of microbiological organisms within the formulation, thereby decreasing the product's shelf life. The presence of microbiological organisms could lead to altered product performance as well as a noxious and rancid odor, especially when the product is exposed to sunlight.
Another concern with paint stripping compositions is how to determine when the composition has rendered at least a substantial portion of the paint removable from the substrate. This determination is important because the paint tends to solidify (i.e., harden) and re-adhere if applied to a substrate for an extended period of time. Of course, after the paint begins to solidify, removal of the paint is more difficult.
Paint stripping compositions which advertise a color change when the stripping action is substantially complete have been developed and are commercially available. However, we have found that these compositions do not function as advertised. We have found that the color change is due to the evaporation of free water from the composition and not due to the substantial completion of the stripping action. In addition, we have found that such compositions which contain a large amount of free water tend to harden on the surface, which makes removal of the composition and paint very difficult.
Thus, the industry is in need of an effective paint removal composition which eliminates or at least minimizes the concerns of shelf life, free water content, environmental and dermal problems, odor, toxicity, hardening of the composition and color change as discussed above.